1. Field of the Invention
This invention relates to methods and apparatus for sleeving a borehole that is partially or totally filled with water.
2. Description of the Prior Art
Pumpable explosives have been in use for many years. Although pumpable explosives are often used in dry boreholes, they are primarily applied in situations where high levels of ground water exist. In many mines, the presence of ground water is so great that it is virtually impossible to remove the water from a borehole. Pumpable explosives, then, are used in boreholes completely or at least partially filled with water. Typically, the explosives are pumped from the bottom of the borehole upward to the top. The water is displaced as the borehole is filled with the explosive.
Often a heavily water saturated geology will have voids, caverns, and fissures. This presents a problem when using pumpable explosives. The fluid nature of the explosive enables the pumpable explosive to migrate out from the borehole to the voids, caverns, or fissures. This results in a loss of explosive product, which is both wasteful and unsafe.
Previously, containment of the pumpable explosive was achieved by two methods. First, the product was prepackaged in a bag form and lowered into the borehole. Packaged products must be smaller than the diameter of the borehole, so less explosive can be placed into the borehole than when the explosive is directly pumped into the borehole. Moreover, the gap left between the package and the edge of the borehole causes the explosive charge to be less efficient due to poor compacting. The second previously known containment method involved casing the borehole with a rigid tube made of cardboard, PVC, or plastic. The explosives were then pumped inside the rigid casing. Again, this method did not offer the benefit of completely filling the borehole, and the rigid tube deflected and diminished the energy of the blast.
U.S. Pat. No. 3,696,703 discloses a blasting agent package that consists of a sleeve and concertina tubes. U.S. Pat. No. 4,572,075 discloses methods and apparatus for loading large drill holes with explosives, although not narrow boreholes exposed to large amounts of water. The technology in the '075 patent is intended for use in large diameter drill holes, using primarily non-pumpable explosives which are applied from the top of the drill hole to the bottom, whereas the present invention introduces pumpable explosives into narrow boreholes from the bottom to the top, with the narrow boreholes' being largely, if not completely, submerged under water. Also, in the '075 patent, the casing is a delivery mechanism for the explosive charges introduced at the top into drill holes where underwater challenges are not addressed, whereas in the present invention the sleeve is a containment means to retain pumpable explosive, introduced from the bottom, in the central core of a watery borehole plagued by fissures and crevices typical of underwater terrain.
Accordingly, a need remains for a way maximally to introduce explosives into a water-saturated borehole that is predictable and cost-effective, and which maximizes the explosive charge and avoids loss thereof.